This invention relates generally to a display system for use in a vehicle, and more particularly to such a display system provided with a fluorescent display tube.
A display system of the type described is used, for example, to indicate or display a set temperature of an air conditioner or the like. There is known such a display system provided with a fluorescent display tube which provides a display clearly visible day and night.
Such a fluorescent display tube comprises a filament coated with an electron-emitting substance, and a plurality of anode electrodes each coated with a fluorescent substance. When the filament is energized and heated, the electron-emitting substance emits the electrons. When a positive voltage is applied to selected one or more of the anode electrodes, the electrons emitted from the electron-emitting substance move toward the selected anode electrodes and collide with the fluorescent substance coated on these anode electrodes. At this time, visible rays of light are emitted from the fluorescent substance to make a required display. Thus, in order to cause the fluorescent display tube to make a display, it is necessary that the electrons be emitted by the energization and heating of the filament.
The conventional display systems provided with such a fluorescent display tube are generally classified into two types. Specifically, in one type, the filament is always kept energized regardless of whether the display system is in a display condition or a non-display condition. In the other type, the filament is energized only in a display condition of the display system, and is kept de-energized in a non-display condition of the display system. The former type is shown in FIG. 1 of Japanese Laid-Open (Kokai) Patent Application No. 142731/85, and the latter type is shown in FIGS. 2 and 3 of this Japanese Laid-Open application.
In the case where the display system of the former type is used in a vehicle, there is encountered a problem that the red-hot filament is viewed in the night in a non-display condition of the display system, and therefore is an eyesore to the driver. Moreover, in this case, when the display system is switched to a display condition (that is, voltage is applied to the anode electrodes), the anode electrodes immediately emit a sufficient amount of visible light to make a bright display since the filament has been preheated red-hot. This is disadvantageous in that a great stimulus is given to the eyes of the driver which have been accustomed to the darkness.
In the display system of the latter type when it is switched from a non-display condition to a display condition, sufficient quantities of electrons are not produced before the filament becomes hot-red, and therefore the amount of visible light emitted from the fluorescent substance is insufficient. This is disadvantageous particularly in the daytime in that the display is unclear.
With respect to other prior art, Japanese Laid-Open Utility Model Application No. 112910/87 discloses a mode selection switch used in an air conditioner, and Japanese Laid-Open Patent Application No. 71215/86 discloses a sensor for detecting the intensity of the sunlight which is used as one of data for controlling the operation of an air conditioner.